Highly fluorinated ionic liquids as boundary lubricants

ABSTRACT

An ionic liquid comprising: a cation (or conjugate acid), wherein the cation (or conjugate acid) is represented by General Formula (A) below or General Formula (B) below or General Formula (C) or General Formula (D) below or General Formula (E) below: 
     
       
         
         
             
             
         
       
         
         
           
             wherein R 1  represents CH 2 CH 2 (CF 2 ) n CF 3 , where n is an integer ranging from 0 to 7, or an alkyl chain CH 3 , or CH 2 OH, or CH 2 CH 2 OH; R 2  represents CH 2 CH 2 (CF 2 ) n CF 3 , where n is an integer ranging from 0 to 7, or a hydrogen atom H, or CH 2 OH, or CH 2 CH 2 OH; and R 3  represents CH 2 CH 2 (CF 2 ) n CF 3 , where n is an integer ranging from 0 to 7.

RELATED APPLICATION

This application claims priority benefit under 35 U.S.C. § 119(e) ofU.S. Provisional Application No. 62/986,536 filed Mar. 6, 2020 thecontents of which are herein incorporated by reference.

FIELD OF THE DISCLOSURE Technical Field

The present disclosure relates to a group of novel highly fluorinatedionic liquids which contain cations with highly fluorinated alkyl chainsand anions with multiple fluorinated components. The present disclosurealso relates to methods of preparing nanometer-thick boundary lubricantscontaining highly fluorinated ionic liquids and the use of highlyfluorinated ionic liquids as next-generation nanometer-thick boundarylubricants.

Background

The physical contact between adjacent solid surfaces has been a hugeconcern for many nanoscale devices with contacting components duringoperation, e. g., hard disc drives (HDDs) and nano-electromechanical andmicro-electromechanical systems (NEMS/MEMS). The use of nanometer-thickboundary lubricants is critical to the efficiency and reliability ofthese devices. Ideally, the lubricants should have high thermalstability due to the increasing temperature during tribology contact,and low monolayer (ML) thickness which determines the minimum thicknessof the lubricants. Additionally, the lubricants should be load-carryingand self-healing, and have low surface tension and excellenttribological property. Unfortunately, the state-of-the-art lubricant,perfluoropolyether (PFPE), only has limited thermal stability, and itsML is relatively thick due to the polymeric chain structure.

Ionic liquids (ILs) are promising candidates for the next-generationmedia lubricants due to their extraordinary physical properties andrelatively low cost. ILs are salts that are in liquid phases at roomtemperature, and they consist of cations and anions. Many ILs havehigher thermal stability and lower volatility over PFPEs. The molecularsizes of ILs are also much smaller than those of PFPEs, making thempossible to achieve lower ML. Moreover, ILs with aromatic rings formlayering structures when confined on solid surfaces, which is ideal forlubrication. Nevertheless, the major concern for conventional ILs asmedia lubricants is their higher surface tension than PFPEs. Thisdrawback significantly limits the tribological performance of ILs asnanometer-thick media lubricants.

BRIEF SUMMARY OF THE DISCLOSURE

In one aspect, the present disclosure relates to the chemicalcompositions of a group of novel highly fluorinated ILs. The highlyfluorinated ILs of the present disclosure contain cations with highlyfluorinated alkyl chains and anions with multiple CF_(x) groups, andconsequently have very low surface tensions. The low surface tensions ofthe highly fluorinated ILs are ideal for their tribological performance.

In another aspect, the present disclosure also relates to the method offabricating nanometer-thick lubricants that consists of highlyfluorinated ILs of the present disclosure by means of a dip coatingprocess. The thickness of the nanometer-thick lubricants can be readilycontrolled by changing the concentration of the bulk solution. The useof the highly fluorinated ionic liquids of the present disclosure as thenext-generation nanometer-thick boundary lubricants is provided.

Many other variations are possible with the present disclosure, andthose and other teachings, variations, and advantages of the presentdisclosure will become apparent from the description and figures of thedisclosure.

A first aspect of a preferred embodiment of the present disclosurecomprises an ionic liquid comprising a cation (or conjugate acid),wherein the cation (or conjugate acid) is represented by General Formula(A) below or General Formula (B) below or General Formula (C) or GeneralFormula (D) below or General Formula (E) below:

wherein R₁ represents CH₂CH₂(CF₂)_(n)CF₃, where n is an integer rangingfrom 0 to 7, or an alkyl chain CH₃, or CH₂OH, or CH₂CH₂OH; R₂ representsCH₂CH₂(CF₂)_(n)CF₃, where n is an integer ranging from 0 to 7, or ahydrogen atom H, or CH₂OH, or CH₂CH₂OH; and R₃ representsCH₂CH₂(CF₂)_(n)CF₃, where n is an integer ranging from 0 to 7.

A second aspect of a preferred embodiment of the present disclosurecomprises an ionic liquid comprising an anion (or conjugate base)comprising bis(trifluoromethanesulfonimide),bis(nonafluorobutanesulfonyl)imide ortris(pentafluoroethyl)trifluorophosphate.

A third aspect of a preferred embodiment of the present disclosurecomprises an ionic liquid comprising an anion (or conjugate base),wherein the anion (or conjugate base) is represented by General Formula(Z) below:

-   -   wherein X represents N(SO₂)₂ with “n” equaling 2 or X represents        PF₃ with “n” equaling 3; and wherein Y represents (CF₂)_(m)CF₃        with “m” equaling 0, 1, 2, 3, 4, 5 or 6.

A fourth aspect of a preferred embodiment of the present disclosurecomprises an ionic liquid comprising a cation (or conjugate acid),wherein the cation (or conjugate acid) is represented by General Formula(A) below or General Formula (B) below or General Formula (C) or GeneralFormula (D) below or General Formula (E):

-   -   wherein R₁ represents CH₂CH₂(CF₂)_(n)CF₃, where n is an integer        ranging from 0 to 7, or an alkyl chain CH₃, or CH₂OH, or        CH₂CH₂OH; R₂ represents CH₂CH₂(CF₂)_(n)CF₃, where n is an        integer ranging from 0 to 7, or a hydrogen atom H, or CH₂OH, or        CH₂CH₂OH; and R₃ represents CH₂CH₂(CF₂)_(n)CF₃, where n is an        integer ranging from 0 to 7; and an anion (or conjugate base)        comprising bis(trifluoromethanesulfonimide) or        bis(nonafluorobutanesulfonyl)imide or        tris(pentafluoroethyl)trifluorophosphate or an anion (or        conjugate base), wherein the anion (or conjugate base) is        represented by General Formula (Z) below:

-   -   wherein X represents N(SO₂)₂ with “n” equaling 2 or X represents        PF₃ with “n” equaling 3; and wherein Y represents (CF₂)_(m)CF₃        with “m” equaling 0, 1, 2, 3, 4, 5 or 6.

An additional aspect of a preferred embodiment of the present disclosurecomprises a lubricant comprising the ionic liquid according to the firstaspect above.

A further aspect of a preferred embodiment of the present disclosurecomprises a lubricant comprising the ionic liquid according to thesecond aspect above.

Another aspect of a preferred embodiment of the present disclosurecomprises a lubricant comprising the ionic liquid according to the thirdaspect above.

An additional aspect of a preferred embodiment of the present disclosurecomprises a lubricant comprising the ionic liquid according to thefourth aspect above.

Yet another aspect of a preferred embodiment of the present disclosurecomprises a magnetic recording medium comprising a non-magnetic support;a magnetic layer on the non-magnetic support; and the lubricantaccording to the first aspect above on the magnetic layer.

In another aspect of a preferred recording medium of the presentdisclosure, the magnetic layer has a carbon overcoat and the lubricantis disposed on the carbon overcoat of the magnetic layer.

Another aspect of a preferred embodiment of the present disclosurecomprises a method of applying an ionic liquid on a surface of a solidsubstrate, such as a magnetic media with a carbon overcoat, comprisingpreparing a dilute solution by dissolving the ionic liquid in2,3-dihydrodecafluoropentane; dipping the solid substrate into thedilute solution vertically at a first rate of travel (mm/min); andwithdrawing the solid substrate vertically from the dilute solution at asecond rate of travel (mm/min).

In another aspect of a preferred method of applying an ionic liquid on asurface of a solid substrate of the present disclosure, the first rateof travel equals the second rate of travel.

In yet another aspect of a preferred method of applying an ionic liquidon a surface of a solid substrate of the present disclosure, each of thefirst rate of travel and the second rate of travel equals 60 mm/min.

In a further aspect of a preferred method of applying an ionic liquid ona surface of a solid substrate of the present disclosure, the first rateof travel is not equal to the second rate of travel.

Another aspect of a preferred embodiment of the present disclosurecomprises a method for making a fluorinated ionic liquid, comprisingdissolving iodide of CH₂CH₂(CF₂)_(n)CF₃ (n=0-7) in Toluene to produce afirst solution; mixing and/or combining a starting material with thefirst solution to produce a first reaction, wherein the startingmaterial is represented by General Formula (F) below or General Formula(G) below or General Formula (H) or General Formula (I) below or GeneralFormula (J):

wherein R₁ represents CH₂CH₂(CF₂)_(n)CF₃, where n is an integer rangingfrom 0 to 7, or an alkyl chain CH₃, or CH₂OH, or CH₂CH₂OH; R₂ representsCH₂CH₂(CF₂)_(n)CF₃, where n is an integer ranging from 0 to 7, or ahydrogen atom H, or CH₂OH, or CH₂CH₂OH; stirring and refluxing the firstreaction at 110° C. under N₂ purging for 15 hours; cooling the stirredand refluxed first reaction to room temperature; decanting Toluene fromthe first reaction to produce a remainder product; stirring theremainder product in diethyl ether; washing the remainder product withdiethyl ether a plurality of times; drying the washed remainder productunder a vacuum overnight; dissolving the dried remainder product inwater at 65° C. to produce a second solution; adding a fluorinated anionto the second solution to produce a metathesis reaction, wherein thefluorinated anion is an anion (or conjugate base) comprisingbis(trifluoromethanesulfonimide) or bis(nonafluorobutanesulfonyl)imideor tris(pentafluoroethyl)trifluorophosphate or an anion (or conjugatebase), wherein the anion (or conjugate base) is represented by GeneralFormula (Z) below:

wherein X represents N(SO₂)₂ with “n” equaling 2 or X represents PF₃with “n” equaling 3; and wherein Y represents (CF₂)_(m)CF₃ with “m”equaling 0, 1, 2, 3, 4, 5 or 6; stirring the metathesis reaction for 3to 4 hours; dissolving the stirred metathesis reaction product in ethylacetate to produce a third solution; washing the third solution with DIwater until its pH 6-7; testing the washed third solution of pH 6-7 onI″ with AgNO₃ in a separated water phase to confirm test is negative;performing rotary evaporation on the washed and tested third solution toextract a final product; and drying the final product in a vacuum at 75°C. overnight to produce the fluorinated ionic liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which:

FIG. 1 shows preferred chemical structures of the imidazolium cations inthe highly fluorinated ILs of the present disclosure;

FIG. 2 shows preferred chemical structures of the pyridinium cations inthe highly fluorinated ILs of the present disclosure;

FIG. 3 shows preferred chemical structures of the pyrrolidinium cationsin the highly fluorinated ILs of the present disclosure;

FIG. 4 shows preferred chemical structures of the ammonium cations inthe highly fluorinated ILs of the present disclosure;

FIG. 5 shows preferred chemical structures of the phosphonium cations inthe highly fluorinated ILs of the present disclosure;

FIG. 6A shows a preferred chemical structure of an anion in the highlyfluorinated ILs of the present disclosure;

FIG. 6B shows a preferred chemical structure of another anion in thehighly fluorinated ILs of the present disclosure;

FIG. 6C shows a preferred chemical structure of yet another anion in thehighly fluorinated ILs of the present disclosure;

FIG. 7 shows preferred chemical structures of the starting compounds forthe synthesis of the highly fluorinated ILs of the present disclosure;

FIG. 8 is a schematic diagram showing fabrication of the nanometer-thickfilms composed of the highly fluorinated ILs according to preferredmethods of the present disclosure;

FIG. 9 shows a preferred reaction sequence for the synthesis of1-1H,1H,2H,2H-perfluorohexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide according to a preferred method of thepresent disclosure;

FIG. 10 shows a ¹H NMR spectrum of1-1H,1H,2H,2H-perfluorohexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide synthesized according to a preferredmethod of the present disclosure;

FIG. 11 shows TGA results of1-1H,1H,2H,2H-perfluorohexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide synthesized according to a preferredmethod of the present disclosure;

FIG. 12 shows nanofilm thicknesses of1-1H,1H,2H,2H-perfluorohexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide on carbon overcoat (COC) at variousconcentrations before and after Vertrel XF washing according topreferred methods of the present disclosure;

FIG. 13 shows surface roughness results of the nanometer-thickperfluorohexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imidewith varying thicknesses on COC according to preferred methods of thepresent disclosure;

FIG. 14 shows friction results of the nanometer-thick1-1H,1H,2H,2H-perfluorohexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide with varying thicknesses on COCaccording to preferred methods of the present disclosure;

FIG. 15 shows a preferred reaction sequence for the synthesis of1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazoliumbis(trifluoromethylsulfonyl)imide according to a preferred method of thepresent disclosure;

FIG. 16 shows a ¹H NMR spectrum of1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazoliumbis(trifluoromethylsulfonyl)imide synthesized according to a preferredmethod of the present disclosure;

FIG. 17 shows TGA results of1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazoliumbis(trifluoromethylsulfonyl)imide synthesized according to a preferredmethod of the present disclosure;

FIG. 18 shows nanofilm thicknesses of1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazoliumbis(trifluoromethylsulfonyl)imide on COC at various concentrationsbefore and after Vertrel XF washing according to preferred methods ofthe present disclosure;

FIG. 19 shows surface roughness results of the nanometer-thick1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazoliumbis(trifluoromethylsulfonyl)imide with varying thicknesses on COCaccording to preferred methods of the present disclosure;

FIG. 20 shows friction results of the nanometer-thick1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazoliumbis(trifluoromethylsulfonyl)imide with varying thicknesses on COCaccording to preferred methods of the present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following description, taken in conjunction with the referenceddrawings, is presented to enable one of ordinary skill in the art tomake and use the disclosure and to incorporate it in the context ofparticular applications. Various modifications, as well as a variety ofuses in different applications, will be readily apparent to thoseskilled in the art, and the general principles, defined herein, may beapplied to a wide range of aspects. The present disclosure is notintended to be limited to the aspects disclosed herein. Instead, it isto be afforded the widest scope consistent with the disclosed aspects.

In HDDs, nanometer-thick lubricants need to be applied on the mediasurfaces in order to reduce direct head-media contact and protect themedia from wear during operations. In NEMS/MEMS, it is desirable to haveultrathin anti-adhesive coatings on the surfaces of thenanoscale/microscale devices to avoid device breakdown. ILs have hugepotential to be the next-generation lubricants in those devices becauseof their small molecular sizes, excellent tribological properties, highthermal stability, negligible volatility, and low cost. Morespecifically, the lubricant thickness can be reduced due to the smallmolecular size of ILs, and the lubricant thermal stability can beenhanced due to the strong electrostatic interactions between thecations and the anions. Another key characteristic of such IL boundarylubrication is the low friction, which is largely determined by thesurface tension of the IL molecules. The surface tensions of theconventional commercially available ILs (>30 mN/m in general), however,is higher than that of the state-of-the-art PFPE lubricants (e. g., 24mN/m for PFPE Zdol), which leads to higher frictions of the ILlubricants than the PFPE lubricants. The relatively high surfacetensions of the current ILs significantly limit their tribologicalperformance.

To address the current issue, the present disclosure relates to thechemical compositions of novel highly fluorinated IL molecules and themethod to apply the highly fluorinated IL lubricants on solid surfaces,e. g., the surfaces of magnetic media. For the molecular design of thenext-generation IL lubricants, it is necessary to add multiple CF_(x)groups in both the cations and the anions of the IL molecules to achievelower surface tensions and better tribological performance, as thestrong C—F bonds and the low polarity in the fluorinated components canlead to weak intermolecular forces, and consequently low surfacetensions. Preferably, the IL molecules of the present disclosure containenough fluorinated components so as to have low surface tensions thatare comparable to the surface tensions of PFPEs, which can result inmuch more robust tribological properties than the current ILs. Thechemical structures of both the highly fluorinated cations and thehighly fluorinated anions have been provided in the present disclosure.The highly fluorinated IL molecules can be random combinations of thepreferred cations and anions of the present disclosure set forth below.

FIG. 1 illustrates the preferred chemical structures of the imidazoliumcations of the highly fluorinated ILs of the present disclosure. In FIG.1 , the IL cation contains an imidazolium ring with multiple sidechains. The side chain R₁ on the nitrogen atom N represents eitherCH₂CH₂(CF₂)_(n)CF₃, where n is an integer ranging from 0 to 7, or analkyl chain CH₃, or CH₂OH, or CH₂CH₂OH. —OH functional groups willprovide bonding between the IL and the solid substrate, e.g., magneticmedia with carbon overcoat (COC). The side chain R₂ on the carbon atom Crepresents either CH₂CH₂(CF₂)₁₁CF₃, where n is an integer ranging from 0to 7, or a hydrogen atom H, or CH₂OH, or CH₂CH₂OH. The side chain R₃ onthe other nitrogen atom N represents CH₂CH₂(CF₂)_(n)CF₃, where n is aninteger ranging from 0 to 7.

FIG. 2 illustrates the chemical structures of the pyridinium cations ofthe highly fluorinated ILs of the present disclosure. In FIG. 2 , the ILcation contains a pyridinium ring with multiple side chains. The twoside chains R₂ on the carbon atoms C represents eitherCH₂CH₂(CF₂)_(n)CF₃, where n is an integer ranging from 0 to 7, or ahydrogen atom H, or CH₂OH, or CH₂CH₂OH. —OH functional groups willprovide bonding between the IL and the solid substrate, e.g., magneticmedia with COC. The two side chains R₂ can be either identical ordifferent. The side chain R₃ on the nitrogen atom N representsCH₂CH₂(CF₂)_(n)CF₃, where n is an integer ranging from 0 to 7.

FIG. 3 illustrates the chemical structures of the pyrrolidinium cationsof the highly fluorinated ILs of the present disclosure. In FIG. 3 , theIL cation contains a pyrrolidinium ring with two side chains on thenitrogen atom N. The side chain R₁ represents either CH₂CH₂(CF₂)_(n)CF₃,where n is an integer ranging from 0 to 7, or an alkyl chain CH₃, orCH₂OH, or CH₂CH₂OH. —OH functional groups will provide bonding betweenthe IL and the solid substrate, e.g., magnetic media with COC. The otherside chain R₃ represents CH₂CH₂(CF₂)_(n)CF₃, where n is an integerranging from 0 to 7.

FIG. 4 illustrates the chemical structures of the ammonium cations ofthe highly fluorinated ILs of the present disclosure. In FIG. 4 , the ILcation contains an ammonium structure with four side chains on thenitrogen atom N. The three side chains R₁ represents eitherCH₂CH₂(CF₂)_(n)CF₃, where n is an integer ranging from 0 to 7, or analkyl chain CH₃, or CH₂OH, or CH₂CH₂OH. —OH functional groups willprovide bonding between the IL and the solid substrate, e.g., magneticmedia with COC. The three side chains R₁ can be either identical ordifferent. The side chain R₃ represents CH₂CH₂(CF₂)_(n)CF₃, where n isan integer ranging from 0 to 7.

FIG. 5 illustrates the chemical structures of the phosphonium cations ofthe highly fluorinated ILs of the present disclosure. In FIG. 5 , the ILcation contains a phosphonium structure with four side chains on thenitrogen atom N. The three side chains R₁ represents eitherCH₂CH₂(CF₂)_(n)CF₃, where n is an integer ranging from 0 to 7, or analkyl chain CH₃, or CH₂OH, or CH₂CH₂OH. —OH functional groups willprovide bonding between the IL and the solid substrate, e.g., magneticmedia with COC. The three side chains R₁ can be either identical ordifferent. The side chain R₃ represents CH₂CH₂(CF₂)_(n)CF₃, where n isan integer ranging from 0 to 7.

FIGS. 6(a)-(c) illustrates the chemical structures of the anions of thehighly fluorinated ILs of the present disclosure. All of the anions arehydrophobic with sufficient fluorinated components. In FIG. 6(a), theanion is bis(trifluoromethanesulfonimide). In FIG. 6(b), the anion isbis(nonafluorobutanesulfonyl)imide with more fluorinated components thanbis(trifluoromethanesulfonimide). In FIG. 6(c), the anion istris(pentafluoroethyl)trifluorophosphate, which has even morefluorinated components than bis(nonafluorobutanesulfonyl)imide.

The highly fluorinated ILs of the present disclosure are obtained by atwo-step synthesis described herein. The first step of the synthesisundergoes a S_(N)2 reaction, where the highly fluorinated alkyl chain,i.e., the side chain R₃, is added in the cation. As shown in FIG. 7 ,the starting compound in the present disclosure can be an imidazole withside chains R₁ and R₂ on the ring, or a pyridine with two R₂ side chainson the ring, or a pyrrolidine with the R₁ side chain on the nitrogenatom N, or an amine with three R₁ side chains on the nitrogen atom N, ora phosphine with three R₁ side chains on the phosphorus atom P.Initially, the iodide of CH₂CH₂(CF₂)_(n)CF₃ is dissolved in Toluene. Thestarting material is added in the solution, and the reaction is stirredand refluxed at 110° C. under N₂ purging for 15 hr. After cooling toroom temperature (RT), Toluene is decanted. The remaining product isstirred in diethyl ether, washed with diethyl ether for several times,and dried under vacuum overnight. The second step of the synthesisundergoes a metathesis reaction, where the highly fluorinated anionreplaces the iodide anion. The product from the first step is dissolvedin water at 65° C. The highly fluorinated anions in the presentdisclosure in the form of the lithium salt or the sodium salt is thenadded, and the reaction is stirred for 3-4 hours. After the metathesisreaction, the product is dissolved in ethyl acetate and washed with DIwater until pH 6-7. The test on F with AgNO₃ in the separated waterphase is negative. Finally, the final product is obtained after rotaryevaporation and vacuum drying at 75° C. overnight.

FIG. 8 shows a preferred method of the present disclosure of applyingthe highly fluorinated IL lubricants on the surfaces of solidsubstrates, such as the magnetic media with COC, by dip coating. First,dilute solutions 10 are made by dissolving the highly fluorinated ILs in2,3-dihydrodecafluoropentane, (commercially known as Vertrel XF), whichcan be obtained from Miller-Stephenson Chemical Company. The highlyfluorinated ILs easily dissolve in the solvent. The solid substrate 12is then dipped into the solution 10 vertically at a preferred first rateof travel “a” of about 60 mm/min and withdrawn vertically at a secondrate of travel “b” which preferably may be the same or different fromthe first rate of travel “a”. The solvent then evaporates immediately,leaving behind a smooth nanometer-thick film 14 of the highlyfluorinated ILs. The lubricant films made of highly fluorinated ILshaving low surface tensions according to the present disclosure. Basedon various lubrication requirements in static/sliding friction,anti-wear, anti-adhesion, and lubricant thickness, the film thicknesscan be precisely controlled by changing the concentrations of thesolutions. For example, lubricant films with sub-ML thickness can befabricated from more diluted solutions, and lubricant films withthickness of several MLs can be fabricated from more concentratedsolutions.

The highly fluorinated ILs of the present disclosure are designed to bethe next-generation nanometer-thick boundary lubricants, whichpreferably are fabricated by means of the dip coating method describedherein with reference to FIG. 8 . The ML thicknesses are reducedcompared to the current media lubricants due to their small molecularsizes. Their tribological performances are improved compared to thecurrent IL lubricants because of their more fluorinated components inthe molecular structures and their lower surface tensions. Moreover, thelayering structure of the solid-confined highly fluorinated ILs is idealfor lubrication. The highly fluorinated ILs of the present disclosureform layering of cations and anions on charged solid surfaces, e. g.,the surfaces of silicon wafer and mica. Highly fluorinated ILs of thepresent disclosure with aromatic rings in the cations also form layeringstructures with enhanced packing efficiency on the surfaces of amorphouscarbon with sp² hybridization, i.e., COC, graphene, and graphite. Inaddition to the use as media lubricants, the nanometer-thick highlyfluorinated ILs are also designed for many other applications, e. g.,the ultrathin anti-adhesive coatings in NEMS/MEMS.

EXAMPLES

The present disclosure includes is not limited to the present examples.In the presented examples, the highly fluorinated ionic liquids weresynthesized and characterized. The nanometer-thick lubricants consistingof the highly fluorinated ILs were fabricated, and then the ML thicknessand friction were presented.

Thermogravimetric analysis (TGA) was performed to determine the thermalstability of the highly fluorinated ILs. These tests were conducted witha SEIKO-220 TG system, using sample weight of ˜25 mg. The samples wereheated from room temperature to 600° C. at a heating rate of 10° C./minin 94% N₂/6% O₂.

The substrate used is COC, on which the nanometer-thick lubricants areapplied in the HDDs. Thicknesses of the nanometer-thick lubricants weremeasured with an Alpha-SE (J. A. Woollam Co.) spectroscopicellipsometer. The incident angle was 70° and the wavelength range was380-900 nm.

AFM imaging was conducted to investigate the surface roughness of thenanometer-thick lubricants on COC. The scans were performed at tappingmode with a Veeco Dimension V Scanning Probe Microscope (256 by 256pixels, 0.1 nm vertical resolution). The AFM probe utilized has analuminum tip on a n-type silicon cantilever (MikroMasch NSC14/AL BS, 160kHz resonance frequency, 5.0 N/m force constant, 8 nm tip radius). Thescan size was 10 μm by 10 μM for all scans, which determined the lateralresolution of 39 nm at 256 pixels.

Tribology testing was performed with a CSM Instruments Nanotribometer(NTR²) on top of a Kinetic Systems antivibration platform. Frictionforce and normal force were measured with a dual beam cantilever andhigh-resolution capacitive sensors. The counterface used was a 2 mmdiameter stainless steel sphere. The normal load was 10 mN, the maximumlinear speed was 0.20 cm/s, the half amplitude was 1.00 mm, and 50cycles were performed. The tests were conducted at 20-22° C. and 6-50%relative humidity.

To understand the bonding interactions between the highly fluorinatedILs and COC, the coated media was washed with pure Vertrel XF with aprocedure similar to dip coating as described herein with reference toFIG. 8 . During this procedure, the coated media was dipped into andwithdrawn from the solvent at 60 mm/min. The thicknesses of theremaining lubricants on COC were then determined by ellipsometry.

Example 1

FIG. 9 illustrates the synthetic path of1-1H,1H,2H,2H-perfluorohexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide. Initially, 21.8 mmol1-Iodo-1H,1H,2H,2H-perfluorohexane was dissolved in 35 mL Toluene. 24.0mmol 1-methylimidazole was added, and the reaction is refluxed at 110°C. under N₂ purging for 15 hr. The first step of the synthesis undergoesa S_(N)2 reaction. After cooling to RT, Toluene was decanted. Theremaining wax was stirred in 200 mL diethyl ether. The wax was washedwith 2×150 mL diethyl ether and dried under vacuum overnight. The solidproduct was then dissolved in 80 mL DI water at 65° C. 21.8 mmol lithiumbis(trifluoromethane)sulfonimidate was then added, and the reaction wasstirred for 3 hr. The second step of the synthesis undergoes ametathesis reaction. Afterwards, the product was dissolved in 200 mLethyl acetate and washed with 4×100 mL DI water until pH 6-7. The teston I″ with AgNO₃ in the separated water phase was negative. Finally, thefinal product was extracted from the solvent by rotary evaporation anddried under vacuum at 75° C. overnight. The obtained1-1H,1H,2H,2H-perfluorohexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide was a viscous liquid.

¹H NMR was conducted on the synthesized1-1H,1H,2H,2H-perfluorohexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide. The spectrum and all the peakassignments are indicated in FIG. 10 , which demonstrates the successfulsynthesis. The peak at 2.5 ppm is from the trace impurities of thesolvent DMSO-d₆, and the peak at 3.3 ppm is from absorbed water in thesolvent. Additionally, as shown in FIG. 11 , only one step of weightloss can be detected by TGA, which further demonstrates the high purityof the product. The TGA result also indicates the excellent thermalstability of the product. The surface tension of the highly fluorinatedIL reduces to 24.5 mN/m based on the pendant drop analysis, as comparedto the 30.8 mN/m surface tension for the commercially available1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

Nanometer-thick lubricants consisting of1-1H,1H,2H,2H-perfluorohexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide was applied on the COC surfaces by thepreferred fabrication method of the current disclosure. As shown in FIG.12 , the thickness of the fabricated nanofilms increases proportionallywith the concentration of the bulk solutions within the investigatedthickness range of nanofilm thickness. FIG. 12 also shows that most ofthe nanofilms of the highly fluorinated IL of the present disclosure canbe washed off the COC surfaces by Vertrel XF, indicating weak bonding ofthe nanofilms to the solid substrates.

ML thickness of the synthesized1-1H,1H,2H,2H-perfluorohexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide was determined by AFM surfaceroughness analysis. FIG. 13 shows the surface roughness results(represented by the root-mean-square roughness, RMS) and thecorresponding AFM images of the highly fluorinated IL with differentthicknesses on COC. The AFM roughness results revealed that the surfacesremained very smooth for nanofilms thinner than ˜0.9 nm, while thesurfaces became much rougher for the nanofilms thicker than ˜0.9 nm.Therefore, 0.9 nm is determined to be the ML thickness of1-1H,1H,2H,2H-perfluorohexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide. The small molecular size of thehighly fluorinated IL of the present disclosure determines the extremelylow ML thickness of the nanofilms.

FIG. 14 presents the friction results of the nanofilms of1-1H,1H,2H,2H-perfluorohexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide. The friction of the bare COC surfaceis used as control. The friction coefficients of the nanometer-thicklubricants consisting of the highly fluorinated IL of the presentdisclosure reached minimum values of ˜0.15 when the nanofilms werethicker than the ML thickness of the highly fluorinated IL.

Example 2

FIG. 15 shows the synthetic path of1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazoliumbis(trifluoromethylsulfonyl)imide. Initially, 21.8 mmol1-Iodo-1H,1H,2H,2H-perfluorohexane was dissolved in 35 mL Toluene. 24.0mmol 1-(2-hydroxyethyl)imidazole was added, and the reaction is refluxedat 110° C. under N₂ purging for 15 hr. The first step of the synthesisundergoes a S_(N)2 reaction. After cooling to RT, Toluene was decanted.The remaining wax was stirred in 200 mL diethyl ether. The wax waswashed with 2×150 mL diethyl ether and dried under vacuum overnight. Thesolid product was then dissolved in 80 mL DI water at 65° C. 21.8 mmollithium bis(trifluoromethane)sulfonimidate was then added, and thereaction was stirred for 3 hr. The second step of the synthesisundergoes a metathesis reaction. Afterwards, the product was dissolvedin 200 mL ethyl acetate and washed with 4×100 mL DI water until pH 6-7.The test on F with AgNO₃ in the separated water phase was negative.Finally, the final product was extracted from the solvent by rotaryevaporation and dried under vacuum at 75° C. overnight. The synthesized1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazoliumbis(trifluoromethylsulfonyl)imide was a viscous liquid.

¹H NMR was conducted on the obtained1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazoliumbis(trifluoromethylsulfonyl)imide. The spectrum and all the peakassignments are indicated in FIG. 16 , which demonstrates the successfulsynthesis. Moreover, the TGA result in FIG. 17 shows only one step ofweight loss, which indicates the excellent thermal stability of thehighly fluorinated IL. The surface tension reduces to 24.8 mN/m based onthe pendant drop analysis, as compared to the 30.8 mN/m surface tensionfor the commercially available 1-hexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide.

Nanometer-thick films of1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazoliumbis(trifluoromethylsulfonyl)imide was applied on the COC surfaces by thepreferred fabrication method of the current disclosure. As shown in FIG.18 , the thickness of the fabricated nanofilms increases proportionallywith the concentration of the bulk solutions within the investigatedthickness range of nanofilm thickness. FIG. 18 also shows that ˜0.4-0.5nm of the highly fluorinated IL nanofilms survived the Vertrel XFwashing, indicating enhanced bonding interactions between the nanofilmsand the solid substrates.

ML thickness of the obtained1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazoliumbis(trifluoromethylsulfonyl)imide was determined by AFM surfaceroughness analysis. FIG. 19 shows the surface roughness results and thecorresponding AFM images of the highly fluorinated IL with varyingthicknesses on COC. The surface roughness results revealed that thenanofilm surfaces remained very smooth when the nanofilms were thinnerthan ˜1.1 nm, while the nanofilm surfaces became much rougher when thenanofilms were thicker than ˜1.1 nm. As a result, 1.1 nm is determinedto be the ML thickness for1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazoliumbis(trifluoromethylsulfonyl)imide. This highly fluorinated IL of thepresent disclosure has the potential to achieve extremely low MLthickness because of its small molecular size.

FIG. 20 shows the friction results of the nanometer-thick1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazoliumbis(trifluoromethylsulfonyl)imide. The friction of the bare COC surfaceis used as control. The friction coefficients of the nanometer-thicklubricants consisting of the highly fluorinated IL of the presentdisclosure approached minimum values of ˜0.15 when the nanofilms grewthicker than the ML thickness of the highly fluorinated IL.

What is claimed is:
 1. An ionic liquid comprising: a cation (orconjugate acid), wherein the cation (or conjugate acid) is representedby General Formula (A) below or General Formula (B) below or GeneralFormula (C) or General Formula (D) below or General Formula (E):

wherein R₁ represents CH₂CH₂(CF₂)_(n)CF₃, where n is an integer rangingfrom 0 to 7, or an alkyl chain CH₃, or CH₂OH, or CH₂CH₂OH; R₂ representsCH₂CH₂(CF₂)_(n)CF₃, where n is an integer ranging from 0 to 7, or ahydrogen atom H, or CH₂OH, or CH₂CH₂OH; and R₃ representsCH₂CH₂(CF₂)_(n)CF₃, where n is an integer ranging from 0 to 7; and ananion (or conjugate base) comprising bis(trifluoromethanesulfonimide) ortris(pentafluoroethyl)trifluorophosphate or an anion (or conjugatebase), wherein the anion (or conjugate base) is represented by GeneralFormula (Z) below:XY_(n) X=

F₃ (n=3)Y═(CF₂)_(m)CF₃ (m=0, 1, 2, . . . )  General Formula (Z) wherein Xrepresents PF₃ with “n” equaling 3; and wherein Y represents(CF₂)_(m)CF₃ with “m” equaling 0, 1, 2, 3, 4, 5 or
 6. 2. A lubricantcomprising: the ionic liquid according to claim
 1. 3. A magneticrecording medium comprising: a non-magnetic support; a magnetic layer onthe non-magnetic support; and the lubricant according to claim 1 on themagnetic layer.
 4. The magnetic recording medium of claim 3, wherein themagnetic layer has a carbon overcoat and the lubricant is disposed onthe carbon overcoat of the magnetic layer.
 5. A method of applying anionic liquid on a surface of a solid substrate, such as a magnetic mediawith a carbon overcoat, comprising: providing the ionic liquid whichcomprise the ionic liquid of claim 1; preparing a dilute solution bydissolving the ionic liquid in 2,3-dihydrodecafluoropentane; dipping thesolid substrate into the dilute solution vertically at a first rate oftravel (mm/min); and withdrawing the solid substrate vertically from thedilute solution at a second rate of travel (mm/min).
 6. The method ofclaim 5, wherein the first rate of travel equals the second rate oftravel.
 7. The method of claim 5 wherein each of the first rate oftravel and the second rate of travel equals 60 mm/min.
 8. The method ofclaim 5, wherein the first rate of travel is not equal to the secondrate of travel.